Broadband spectrum illumination sources are commonly implemented in spectroscopic based optical metrology tools. Such broadband based metrology tools may be utilized to measure various parameters associated with a given sample, such as a semiconductor wafer or lot of semiconductor wafers. Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Broadband based metrology systems may include, but are not limited to, spectroscopic ellipsometry, reflectometry, or scatterometry based systems. For example, a broadband based metrology system may include a system such as a rotating polarizer ellipsometry (RPE) or a rotating analyzer ellipsometry (RAE). Typically, a broadband based metrology tool includes one or more broadband light sources, such as a Xenon lamp, illumination optics, a sample stage, collection optics, and one or more detectors. In a general sense, broadband based metrology systems may include an illumination source capable of emanating light within the range of deep ultraviolet (DUV) to near infrared (NIR).
Metrology processes are used at various steps during a semiconductor manufacturing process to monitor and control one or more semiconductor layer processes. For example, broadband based metrology may be used to measure characteristics of a thin film deposited or grown on the surface of a semiconductor wafer, as well as patterned features formed on the semiconductor wafer. By sampling light reflected from a semiconductor wafer at a detector as a function of angle of incidence (AOI), azimuthal angle, polarization, and wavelength, information related to the physical properties of the wafer may be gathered. Such features include, but are not limited to, film thickness, dispersion within the film, wafer structure shapes, and critical dimension (CD) of structures of the wafer.
Typically, the illumination source of a given broadband spectrometry based metrology system is coupled to the collection optics of the system via optical fiber. FIG. 1 illustrates an example of a system implementing optical fiber to couple an illumination source to a portion of the collection optics. The system 100 includes, for example, an optical fiber 102, a pair of mirrors 106a and 106b, and a rotating polarizer 108. In this sense, the optical fiber 102 is utilized to present light 104 from a broadband source (not shown) to the illustrated portion of the collection optics. The utilization of optical fiber to couple a broadband source to collection optics aids in improving pointing stability and intensity fluctuations created due to beam pointing errors. Moreover, optical fiber may act as a light scrambler, causing the intensity spatial distribution of the transmitted light to become more uniform as it propagates through the optical fiber. Further, the spatial dimension of the illumination source (as it is presented to the collection optics) is defined by the physical diameter of the optical fiber. As such, optical fiber plays a key role in both beam shaping and beam stabilization.
The UV throughput capabilities of optical fiber, however, degrade over time, due to solarization and UV enhanced photocontamination. This degradation leads to increased spectral instability and decreased system lifetime. The degradation of UV throughput may lead to a narrowing of the transmitted spectral range, as light below approximately 230 nm (UV boundary) displays reduced transmittance. As such, the UV throughput degradation leads to a modification of the transmitted broadband light. Consequently, it is desirable to provide a system and method that couples a broadband source to collection optics without optical fiber coupling.